Stephen Hawking isn't shy about giving the world a reality check. The world-renowned British theoretical physicist, whose work has revolutionized our understanding of black holes and the physics of the cosmos, is a realist who often discusses his fears for humanity's future.

In a talk at Oxford University on Nov. 14, Hawking tackled some big questions, such as the origins of the universe and why we even exist, but he also reminded the audience at the historic Oxford Union debate hall that our civilization has a sell-by date. At least, it has a sell-by date if we remain on Earth.

Hawking is an outspoken proponent of space exploration. Of particular interest is Hawking's excitement for our species to leave Earth and spread throughout the solar system and, possibly, beyond. Though our thirst for knowledge is one of the fundamental drivers pushing humanity to explore the universe, Hawking sees settling on alien worlds as an insurance policy for our species, countering our ever-looming existential threat. After all, should the worst happen to Earth, wouldn't it be great if we at least have people already living somewhere else?

His enthusiasm for interstellar travel, for example, was recently highlighted when he backed the Breakthrough Starshot project, which is part of the $100 million Breakthrough Initiative. Starshot aims to initiate the development of technologies that could see laser-propelled "nanoprobes" set sail beyond the solar system and toward Alpha Centauri.

The even closer target of Proxima Centauri, which is the sun's nearest stellar neighbor only 4.2 light-years away, is known to play host to an Earth-sized potentially habitable exoplanet. Using current propulsion techniques, it would take us tens of thousands of years to get there, so we need novel technologies to get us there faster if destinations like Proxima b can be used for future human colonies.

This reinforces Hawking's previous warnings that we need to be exceedingly careful not to screw things up in the near term as to create self-sustaining colonies beyond Earth, it's going to take at least another hundred years to set up home on another planet in the solar system and longer if we are to take aim at interstellar targets.

"Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time, and becomes a near certainty in the next thousand or ten thousand years," Hawking said during his BBC Reith Lecture in January. "By that time we should have spread out into space, and to other stars, so a disaster on Earth would not mean the end of the human race.

"However, we will not establish self-sustaining colonies in space for at least the next hundred years, so we have to be very careful in this period."

Hawking identifies human-driven climate change, asteroid strikes, the rise of artificial intelligence and a deadly outbreak as being the key threats to civilization. The upshot is that although the advancement of technology can possibly curtail some of the biggest threats to humanity, technology itself could undermine our very existence.

Although Hawking's dire warnings about the future of humanity always takes center stage, he was keen to end on a high note and motivate his audience to never lose their wonderment about the mysteries of the universe "Remember to look up at the stars, not at your feet. Try to make sense of the wonder that is around you," he said on Monday's talk. "No matter how difficult life may seem, there is always something you can do and be good at."